A) Field of the Invention
The present invention relates to a production process for semiconductor devices such as light emitting diode.
B) Description of the Related Art
Commonly, a light emitting diode (LED) is produced by forming a semiconductor multilayer film (semiconductor layer) consisting of an n-type layer, active layer (light emitting layer), p-type layer, etc., on a substrate and subsequently forming electrodes on the surfaces of the substrate and the semiconductor multilayer film. In the case of using a growth substrate of an insulating material, an appropriate region of the semiconductor layer is etched by, for instance, reactive ion etching to expose part of the n-type layer, followed by forming an electrode in the n-type layer and another electrode in the p-type layer.
The selection of the material for the growth substrate can have a large influence on the crystal quality of the resulting semiconductor layer. The electric conductivity, thermal conductivity, and light absorption coefficient of the growth substrate, however, can also have an influence on the electric, thermal, and optical characteristics of the resulting light emitting diode. It cannot be expected that a growth substrate suitable for forming a semiconductor layer with good crystal characteristics always serves to produce a semiconductor device that is also good in all other characteristics. Some studies have proposed thin-film LEDs or laser diodes (LDs) that are produced by peeling off the semiconductor layer from the growth substrate and forming electrodes directly on the semiconductor layer that contributes to light emission (for instance, see Domestic re-publication of PCT international application WO98-14986 as Patent document 1, Japanese Unexamined Patent Publication (Kokai) No. 2005-516415 as Patent document 2, Japanese Unexamined Patent Publication (Kokai) No. 2000-228539 as Patent document 3, and Japanese Unexamined Patent Publication (Kokai) No. 2004-172351 as Patent document 4). The removal of the growth substrate improves electric, thermal, and optical characteristics. The laser lift-off technique is generally used for the removal of the growth substrate.
Some documents have disclosed inventions of semiconductor device production processes that comprise forming a void-containing layer on a growth substrate, growing an n-type layer, light emitting layer, and p-type layer on it, bonding a support substrate, and then applying an impact to the void-containing layer to peel off the growth substrate (for instance, see Japanese Unexamined Patent Publication (Kokai) No. 2010-153450 as Patent document 5). For the invention described in Patent document 5, a void-containing layer is formed by alternately performing a step for preferred growth in the horizontal direction (in-plane direction of the layer) and a step for preferred growth in the vertical direction (thickness direction of the layer). The openings in the void-containing layer are closed by an n-type layer formed on the void-containing layer.
The semiconductor device production process proposed in Patent document 5 sometimes suffers from a problem as described below.
FIGS. 4A to 4C are cross sections containing a void-containing layer. The problem with the conventional processes is described below with reference to FIGS. 4A to 4C.
Refer to FIG. 4A. A void-containing layer 51 of GaN is located on a growth substrate 50. A material gas G is being supplied to form an n-type layer 52, which is an n-type GaN film, on the void-containing layer 51. Voids 53 are being generated in the void-containing layer 51 and in the n-type layer 52 that is being formed. In this figure, R denotes the openings of the voids 53.
The voids 53 are being closed as the n-type layer 52 grows in the horizontal direction. At the same time, nitrogen gas (N2) resulting from the decomposition of the semiconductor and the GaN crystals 54 in the voids 53 gets out of the voids 53 through the openings R.
Refer to FIG. 4B. FIG. 4B illustrates a later state of the n-type layer 52 formation following the state in FIG. 4A. The voids 53 are closed as a result of the growth of the n-type layer 52. The voids 53 contain GaN crystals 54 remaining inside. The desorption and decomposition of the semiconductor material and GaN crystals 54 continue in the voids 53 after the voids 53 are closed.
Refer to FIG. 4C. FIG. 4C illustrates a later state of the n-type layer 52 formation following the state in FIG. 4B. Ga melts 55 and N2 gas 56 are generated in the voids 53 as the semiconductor material and GaN crystals 54 desorb and decompose in the voids 53 after the closure of the voids 53. The N2 gas 56 generated acts to increase the pressure in the voids 53. There have been problems with this rise in pressure, which can cause, for instance, peeling of the growth substrate 50 during the formation of the n-type layer 52 etc., leading to a decrease in yield. In the voids 53, in particular, the desorption and decomposition of the GaN crystals 54 remaining on the growth substrate 50 (bottom face of the voids 53) do not contribute to the formation of the voids 53, but act to increase the pressure in the voids 53.